The present invention relates generally to removal of markings from integrated circuit packages, and more specifically to de-marking laser-marked thin packages by covering the marked surface with a material suitable for re-marking, as well as to de-marked packages so fabricated.
It is known in the art to apply markings to surfaces of integrated circuits packaged in filled-polymer, transfer-molded packages as well as to other packages; such as preformed ceramic packages into which an integrated circuit (IC) die is inserted. Marking techniques known in the art include ink-marking, wherein a package surface is stamped or rolled with a wet ink mark, and laser marking, wherein a package surface receives identification indicia actually engraved therein with a laser beam. Ink marking is relatively slow, requires periodic changing of the applicator to change marking indicia as well as cleaning of the applicator as ink accumulates thereon, and requires drying of the ink after application. Further, ink marks may smudge or subsequently be abraded off of the package surface. As a consequence, use of laser marking is becoming more prevalent due to the speed of marking, the indelibility of the mark once applied, and the ability to readily change the marking indicia to be applied through a re-programming of the computer controlling movement of the laser beam or a mirror or mirrors reflecting same to the package surface. One particularly efficient laser-marking apparatus is disclosed in pending U.S. patent application Ser. No. 08/590,919, filed Jan. 24, 1996 by the present inventor and assigned to the assignee of the present invention.
Sometimes it becomes necessary to remove marks previously applied to an IC package. In the case of ink-marked IC packages, removal is relatively easily effected using solvents or a mild abrasive action which scrubs the package surface without removing package material. However, in the case of a laser-marked IC package, a preferred method of removal is abrasive removal, wherein a layer of package material is removed from the package surface to a depth sufficient to remove the engraved laser mark, and preferably in a manner to provide a reflective surface suitable for re-marking. Such a method and apparatus for effecting same is disclosed in co-pending U.S. patent applications Ser. Nos. 08/907,962 and 08/909,187, each filed Aug. 11, 1997 by the present inventor and Tony T. Ibarra and assigned to the assignee of the present invention.
There are some widely-employed, thin IC package configurations which are not, however, readily susceptible to abrasive engraved mark removal. In such configurations, the thickness of the package material between the marked package surface and a surface of the IC die within the package is insufficient to permit mark removal by a subtractive technique involving removal of package material to a depth at least equivalent to the bottoms of the engraved markings without compromising package integrity. Wire-bonded IC dice with wire loops extending above the active surface of the IC die and well into the package material present particular challenges to abrasive mark removal. In some extreme cases, the forces involved in abrasive removal will simply destroy the package and enclosed IC.
One such example of a thin plastic package configuration presenting the above-mentioned de-marking problem is a so-called Thin Small Outline Package, or TSOP. Another is a Thin Quad Flat Pack, or TQFP. Such packages are dimensioned with a total package thickness, excluding lead fingers, of less than about one-half the thickness of a plastic Small Outline J-lead package, or SOJ. In terms of actual filled-polymer package dimensions, a TSOP or TQFP plastic package may be less than 0.040 inch in thickness, leaving little or no margin for removal of package material above the active surface of the encased IC die.
Thus, when it is necessary or desirable to de-mark a thin, laser-marked plastic package without damage thereto and in a manner which will facilitate subsequent re-marking, the prior art is devoid of an adequate solution.